Biolubricants, also known as bio-based lubricants or bio-lubes, are typically made from a variety of vegetable oils, such as rapeseed, canola, sunflower, soybean, palm, and coconut oils. The best application for biolubricants is in machinery that loses oil directly into the environment during use, total loss lubricants (TLLs), and in machinery used in any sensitive areas, such as in or near water. Applications for TLLs include two-stroke engines, chainsaw bars and chains, railroad flanges, cables, dust suppressants, and marine lubricants.
Compared to petroleum-based lubricants, use of biolubricants: (1) Produces a cleaner, less toxic work environment and fewer skin problems for those working with engines and hydraulic systems; (2) offers better safety due to higher flashpoints, constant viscosity, and less oil mist and vapor emissions; (3) produces fewer emissions due to higher boiling temperature ranges; (4) are highly biodegradable; and (5) costs less over the product's life-cycle due to less maintenance, storage and disposal requirements.
The use of biolubricants can reduce pollution in stormwater from leaks in engines, hydraulic systems, and brake lines. Many European countries now require biolubricants in selected environmentally sensitive areas.
Since biolubricants outperform petroleum lubricants, less is required per application. Cost benefits include reductions in environmental and safety penalties in the case of spills, and less parts wear, maintenance costs, and disposal fees. Biolubricants evaporate slower than petroleum lubricants and adhere better to metal surfaces. They have several disadvantages in the use phase of the product life cycle, including some bad odors if contaminants are present, high viscosity at low temperatures and poor oxidative stability at high temperatures, although additives designed specifically for plant-based lubricants eliminate stability issues related to extreme high and low temperatures.
More than 50 percent of all lubricants used are estimated to end up in the environment. This would amount to more than 1.25 billion gallons in the U.S. based on a 2006 National Petroleum Refiners Association Report. Although most biolubricants contain a small percentage of additives that are not biodegradable, the quantity of toxins present is significantly less than petroleum lubricants. Thus, used, accidentally spilled, or leaked biolubricants will not contaminatestreams nor kill vegetation and wildlife.
The lubricants (engine and non-engine) and process fluids industries today are searching for materials that are biodegradable. Biodegradability means that the lubricants and process fluids (hereinafter “fluids”) degrade over a period of time, which may be measured by tests such as those promulgated by the Organization of Economic Co-Operation and Development (OECD), including OECD 301B and OECD 301F. Recently, interest has been increasing in fluids which are not only biodegradable, but also renewable. Renewable products contain, by definition, high levels of renewable carbons, and standards are being set to encourage increasingly greater levels of renewability. For example, the European Ecolabel now requires that hydraulic fluids must contain at least 50 percent by weight renewable carbons.
Researchers have attempted to meet requirements or recommendations for both biodegradability and renewability by including in their fluids formulations a variety of types of natural and synthesized oils. Unfortunately, many of these materials exhibit pour points that are too high to enable use in certain important applications. The pour point is the lowest temperature at which the fluid will flow, and pour points below 0° C., desirably below −10° C., more desirably below −15° C., and even below −25° C., are often necessary. These materials in many cases also suffer from poor thermo-oxidative stability at high temperatures (for example, above 90° C.), which may in some cases be due to the amount of unsaturation present in the acid fraction of their chemical structures.
Also, due to increasing environmental concerns, there has been considerable interest in developing lubricant and grease compositions based on renewable resources. Conventional lubricants and greases are based on petroleum derived hydrocarbons that have been viscosified with lithium soaps such as lithium stearate and lithium 12-hydroxystearate. The same technology has been applied to the manufacture of lubricants and greases based on natural oils, particularly soybean oil. Several disadvantages are inherent with this technology. The lithium soaps are difficult to dissolve in the soybean oil, and precise viscosity control is difficult. The viscosity and other properties of the lubricant are controlled by the fatty acid structure requiring a variety of different lithium soaps to be synthesized.
Biolubricants are of increasing interest for a number of reasons including: (1) they are a renewable resource, (2) their production is less dependent on geopolitical considerations, (3) they provide the possibility of a direct replacement of petroleum-based lubricants in existing vehicles, and (4) the net greenhouse gas emissions can be substantially reduced by virtue of CO2 uptake by biolubricant precursors-particularly in the case of cellulose feedstocks.
An easily-obtainable biolubricant is a naturally occurring vegetable oil, which largely comprises triglycerides and some free fatty acids. The properties of vegetable oil, however, make it generally inappropriate for use as a direct replacement for petroleum lubricants in vehicle engines, as the vegetable oils' viscosities may not be adequate and the potential exists for leaving damaging carbon deposits. Additionally, vegetable oils tend to gel at lower temperatures, thereby hindering their use in colder climates.
It is also worth noting that unsaturation in the fatty acid contributes to poor oxidation stability and deposits, and that while hydrogenation will generally improve the oxidation stability of the lubricant, it can make the already poor low temperature performance of the lubricant even worse.
Additionally, lubricants derived from renewable feedstocks such as animal or vegetable oils or fats would be desirable to help reduce the dependence of the United States on foreign oil. Lubricating oils based on renewable sources such as vegetable and animal oils and fats have a number of advantages. The vegetable and animal oils or fats contain triglycerides having ester carbonyl groups. The polar nature of these ester carbonyl groups leads to strong adsorption on metal faces as a very thin film so that the film forming properties of triglyceride based lubricants are particularly advantageous in hydraulic systems. Vegetable oils and animal oils typically have high viscosity indices that facilitate their use over wide temperature ranges. Furthermore, they typically have high fume points (e.g., about 2000 C) and high flash points (e.g., about 3000 C).
In addition, vegetable and animal oil and fat based lubricants help reduce the depletion of fossil-derived hydrocarbons. Moreover, vegetable oil based lubricants are typically biodegradable, which would help reduce the introduction of waste lubricants into the environment. Currently, about 50% of mineral lubricants used worldwide end up in landfills and the like.
However, there are major problems in using oils from renewable feedstocks such as plant oils, (i.e. soybean oils and other vegetable oils), or oils or fats derived from animal sources, (e.g. menhaden, lard, butterfat and other animal derived oils) as lubricants, including: (1) low oxidative stability; (2) relatively low viscosities; and (3) tendencies to solidify at low operating temperatures as manifested by relatively high pour points (temperatures below which they will no longer pour).
Therefore, there is a need for a lubricant based on a renewable feedstock that could be modified to provide the desired properties.
The present invention overcomes these disadvantages inherent in the prior art by providing natural oil based lithium lubricants that do not require the addition of gellants. The compositions are provided by a simple economical process that allows precise viscosity control of the lubricants.